1. Field of the Invention
The present invention relates to a projection aligner for use in a large-scale integrated circuit (LSI) manufacturing process. Moreover, the present invention relates to an aberration estimating (or evaluating) mask pattern for estimating aberration included in an optical system of a projection aligner, an aberration quantity (namely, quantity-of-aberration) estimating method, and an aberration eliminating filter for eliminating the aberration. Furthermore, the present invention relates to a semiconductor manufacturing method for manufacturing a semiconductor device by transferring a circuit pattern while eliminating the aberration.
2. Description of the Related Art
Projection aligners for projecting a circuit pattern of a semiconductor device, which is formed on a mask, onto a wafer are required to have high resolution so as to achieve the transferring of a micro or fine pattern thereon. Generally, in proportion as the numerical aperture (NA) of a projection lens (or projecting lens) increases, or in proportion as the wavelength of exposure light decreases, the resolution is improved. The method of increasing the NA of the projection lens, however, causes a reduction in the focal depth (namely, the depth of focus) thereof at the time of transferring the pattern. Thus, there is a limit to the improvement of the resolution. On the other hand, the use of exposure light having short wavelength requires an extensive modification of the transferring process. The method of decreasing the wavelength of exposure light is, therefore, unpractical.
Thus, in Japanese Patent Laid-Open Nos. 4-251914 and 4-179213, there have been proposed projection aligners, by each of which the resolution can be enhanced by increasing the NA but, simultaneously, the focal depth can be enlarged, by the applicant of the present application. As illustrated in FIG. 19, in this projection aligner, a fly-eye lens 3 is placed diagonally to the front of a lamp house or lamp housing 1 by interposing a mirror 2 therebetween. Further, an aperture 4 is positioned in front of the fly-eye lens 3. Moreover, a blind 6 is placed in front of the aperture 4 by putting a condensing lens or condenser lens 5 therebetween. Furthermore, a photomask 10, on which a desired circuit pattern is formed, is disposed diagonally to the front of the blind 6 by interposing a condensing lens 7, a mirror 8 and a condensing lens 9 therebetween. In addition, a wafer 12 is placed in front of the photomask 10 by interposing a projection optical system or projecting lens system 11 therebetween. The contrast of an image at the time of defocusing is improved by putting a phase shift member, which is operative to cause a phase difference between light passing through the central portion of a transmitting zone or area and light passing though the peripheral area thereof, onto the pupillary surface or pupil plane of the projection optical system 11. Consequently, the focal depth is increased effectively.
However, in the case of the aforementioned conventional projection aligner, the aberration of the optical system is not taken into consideration. Generally, actual or practical optical systems have various aberrations. Typical aberrations are a spherical aberration, an astigmatism aberration, a field curvature and a coma aberration. It is known that theses aberrations can be expressed, as illustrated in FIGS. 20A to 20E, by being converted into wavefront aberrations, respectively. In these figures, xcfx86 denotes a shift quantity or distance of a wavefront; xcfx81 a radius on a pupillary surface (namely, a xcex7"xgr"-plane); xcex8 an angle of rotation with respect to the axis xcex7; y0 coordinates on a wafer surface; and B to F constants. The details of these aberrations are described in various literatures, for example, xe2x80x9cPrinciple of Optics I to IIIxe2x80x9d (published by Tokai University Press.).
Because the optical systems of the conventional projection aligners have such aberrations, the conventional projection aligners have the problems that the image quality thereof is degraded and that the accuracy of transferring a circuit pattern is deteriorated.
The present invention is accomplished to solve such problems of the conventional projection aligners.
Accordingly, an object of the present invention is to provide a projection aligner which can eliminate the influence of the aberrations of the optical system thereof and can achieve the high-accuracy transfer of a (circuit) pattern.
Moreover, another object of the present invention is to provide an aberration estimating mask pattern for estimating the aberration of the optical system of a projection aligner, and to further provide a method for estimating an aberration quantity by using this aberration estimating mask pattern.
Furthermore, still another object of the present invention is to provide an aberration eliminating filter for compensating for an aberration of the optical system of the projection aligner.
Additionally, yet another object of the present invention is to provide a semiconductor manufacturing method for manufacturing a semiconductor device by transferring a circuit pattern while eliminating the influence of the aberration of the optical system of a projection aligner.
To achieve the foregoing objects, in accordance with an aspect of the present invention, there is provided a projection aligner which comprises: a light source; an aperture for shaping illumination light and forming a secondary light source plane; a blind having an opening portion for setting an exposure area; a photomask which has a circuit pattern and is illuminated with illumination light emanating from the secondary light source plane; a projection optical system for projecting a circuit pattern of the photomask by forming an image on an exposed substrate from diffraction light diffracted by the photomask; and an aberration eliminating filter, placed on a pupillary surface of the projection optical system, for eliminating an aberration.
Further, in accordance with another aspect of the present invention, there is provided an aberration estimating mask pattern which comprises: a transparent substrate; a plurality of micro patterns selectively formed on the transparent substrate; and a plurality of larger patterns which are formed selectively on the transparent substrate. Further, in this aberration estimating mask pattern, each of the micro patterns and a corresponding one of the larger patterns are combined with each other. Furthermore, a plurality of such combinations (or sets) of micro patterns and a larger pattern are placed on the transparent substrate.
Moreover, in accordance with a further aspect of the present invention, there is provided an aberration quantity (namely, a quantity-of-aberration) estimating method which comprises the steps of: exposing aberration estimating mask patterns; observing a plurality of finished (or obtained) patterns; finding a best focus position or a finishing position of each of the patterns; and estimating a quantity of an aberration from a quantity of a change in the best focus position or in the finishing position of each of the patterns.
Furthermore, in accordance with yet another aspect of the present invention, there is provided an aberration eliminating filter that is a filter, which is placed on a pupillary surface (namely, a pupil plane) of a projection optical system, for eliminating an aberration. This filter is provided with a transparent substrate and a wavefront regulating (or adjusting) transparent multi-layer film formed on at least one principal plane.
Additionally, in accordance with a further aspect of the present invention, there is provided a semiconductor manufacturing method which comprises the steps of: forming a secondary light source plane by shaping illumination light emanating from a light source; establishing an exposure area; illuminating a photomask with illumination light emanating from a secondary light source plane; forming an image of a light source on a pupillary surface from light diffracted by the mask; compensating a wavefront aberration on the pupillary surface of a projection optical system; and manufacturing a semiconductor device by projecting a circuit pattern onto a wafer.